The present invention is in an agent based on ferrosilicon for the treatment of cast iron melts which are subsequently passed on to a further treatment with spheroidal graphite-inducing elements, especially magnesium.
The structure of cast iron with spheroidal graphite is dependent to a large extent on the nature of the added materials, the carrying out of the melting (overheating temperature and time), the treatment with spheroidal graphite-inducing elements, especially magnesium, and possibly to an after-inoculation.
Numerous publications have addressed the subject of achieving optimum structures by the treatment of cast iron melts. For example, EP-PS 0 175 934 is concerned with an inoculation alloying on the basis of ferrosilicon or silicon with contents of 0.1 to 10% by weight of barium and/or zirconium, less than 2.0% by weight of aluminium and less than 0.3% by weight of calcium. DE-OS 38 09 315, describes a similar alloy, the barium content of which can, however, vary between 0.1 and 15% by weight and which, instead of zirconium, contains from 0.1 to 10% by weight of strontium, as well as less than 2% by weight of aluminium and less than 2.5% by weight of calcium. EP 0 353 804 A1 discloses a process for the production of cast iron with spheroidal graphite by the treatment of cast iron melts with an agent containing magnesium or magnesium and rare earth metals in which the components contained therein correspond to the ratio of the alloy components in the cast iron alloy to be treated. Furthermore, in DE-OS 39 32 162, there is disclosed an agent for the production of spheroidal graphite iron based on magnesium silicide. Finally, it has already been recommended to improve the nucleus state of cast iron melts before the magnesium treatment by the addition of a graphitic inoculation agent (see Giesserei-Praxis, 7, 120-124/1991; C. R. Loper, Jr., B. Y. Hus and T. H. Witter).
However, all the above-mentioned agents have, in particular, the disadvantage that their pre-inoculation effect is relatively small so that a relatively high use of alloy is necessary in order to achieve the desired effect.
Therefore, it is an object of the present invention to provide an agent for the treatment of a cast iron melt which substantially improves the nucleus state of the base melt so as to provide favourable prerequisites for the subsequent treatment with spheroidal graphite-inducing elements.
It is also an object of the present invention to provide an agent which can be introduced into the cast iron melt in a simple manner. It is a further object of the invention to provide an agent which can be dissolved rapidly in the iron melt without slag formation. Another object of the present invention is to provide an agent which can be dispersed uniformly in the melt.
It is yet another object to provide an agent which forms thermodynamically stable substrates, for example Ce.sub.2 O.sub.3 or Ce.sub.2 O.sub.2 S, which remain as nuclei for the crystallisation of the graphite in the melt also during subsequent treatment steps, especially with magnesium.